Propylene polymerization over titanium–magnesium catalysts: The effect of internal and external stereoregulating donors on the number of active centers with different stereospecificity and their reactivity in propagation reaction

Abstract

The combination of the method for measuring of the number of active centers by quenching of polymerization by radioactive carbon monoxide with fractionation of polymers obtained by TREF method (temperature rising elution fractionation) to the separate fractions with different isotacticity has been used for determination of the number of active centers with different isospecificity (CPi) responsible for the formation of Fi fractions as well as for calculation of propagation rate constants (kPi) for these centers.Data on the effect of catalyst composition on the CPi and kPi values have been obtained for the first time for polymerization with three types of titanium-magnesium catalysts with different internal stereoregulating donors (di-n-butyl phthalate – TMC-D, 2,3-di-iso-butyl-diethyl succinate – TMC-S, 9,9-bis(methoxymethyl)-fluorene – TMC-F) and for catalytic system TMC-D with external stereoregulating donor – cyclohexylmethyl(dimethoxy)silane.The possible structures of active centers with different isospecificity are discussed on the base of experimental data obtained on the CPi and kPi values.